1. Field
The present application concerns a dental handpiece for the treatment of root canals and the measurement of the root canal length.
2. Description of Prior Art
Such a handpiece is part of a device for the determination of the length (depth) of a root canal and of the position of the treatment instrument attached to the handpiece, respectively. The device comprises, together with the handpiece, two electrodes and a control and evaluation unit. The first electrode, usually in the form of a clip-on electrode, is attached to the oral mucosa of the patient. The instrument attached to the handpiece, for example a file moving back and forth (executing reciprocating movements), a reamer or a rotating dental drill, serves as the second electrode. Both electrodes are connected to the control and evaluation unit. The control and evaluation unit is connected to a current source, which generates a measuring signal, and furthermore includes a measuring device, preferably a measuring circuit, which determines the length of the root canal and the position of the dental instrument, respectively, on the basis of the change in the electrical resistance or the change in the impedance of the measuring signal between the two electrodes.
From EP 1 444 966 A1, a handpiece is known with which the signal line is implemented by a conducting wire outside of the handpiece, the wire being connected to the dental instrument, serving as the second electrode, with a clip-on connection and a clip holder. The disadvantage with this arrangement is the conducting wire is attached to the sleeve of the handpiece handle, which restricts the manageability of the handpiece.
In order to avoid this disadvantage, handpieces are manufactured with which conductors or components of the handpiece implement the signal line within the handpiece. DE 197 02 370 A1 (DE '370 A1) discloses an arrangement of conducting wires within the handpiece or in the sleeve of the handpiece which make contact with the instrument serving as an electrode by way of a contact device. In the DE 195 20 765 A1 (DE '765 A1) components serving for the transmission of the drive power, especially shafts and gears, parts of the outer sleeve and components in contact with these components are used for signal transmission.
With both designs, it is necessary that at least parts of the outer sleeves are insulated in order to prevent the impairment of the measuring circuit due to contact between the handpiece and the oral cavity of the patient or the hand of the user. Insulation may be achieved by manufacturing part of the handle from plastic, as seen in the DE '370 A1. Alternatively, an insulating film can be attached to the outer surface of the outer sleeve, as explained in connection with the DE '765 A1.
These known handpieces have the disadvantage on the one hand of the greater manufacturing costs due to the coating and on the other hand that plastics used for coating or as a material for the handle sleeve sections are not stable relative to the prevailing ambient conditions for sterilization, particularly steam-sterilization. Since however the handpieces must be sterilized following each use, the life of such coatings or handle sleeve sections is very limited.
The present application is therefore in response to the need for a dental handpiece for the treatment of root canals and the measurement of the root canal length while at the same time avoiding the disadvantages discussed above. In particular, the handpiece must be insensitive to the prevailing ambient conditions for sterilization.